<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>2.7 CSS3画太极阴阳图</title>
    <style>
        body{
            background-color: #ccc;
        }
        #taiji{
            width:150px;
            height: 300px;
            margin: 100px auto;
            border-radius: 50%;
            background-color: white;
            border-left: 150px solid black;
            position: relative;
        }

        #taiji::before{
            content:'';
            position: absolute;
            width: 0px;
            height: 0px;
            padding: 25px;
            border-radius: 50%;
            border: 50px solid black;
            background-color: white;
            left: -75px;
        }

        #taiji::after{
            content:'';
            position: absolute;
            width: 0px;
            height: 0px;
            padding: 25px;
            border-radius: 50%;
            background-color: black;
            border: 50px solid white;

            left: -75px;
            bottom: 0px;
        }

    </style>
</head>
<body>
  <div id="taiji"></div>
</body>
</html>